1. Field of the Invention
The present invention relates in general to a rubber hose and in particular to a rubber hose suitable for use as, for example, a fuel transporting hose for a motor car engine.
2. Discussion of the Prior Art
There is known a fuel conducting or transporting rubber hose having a heat-resistant and gasoline-resistant inner tube, a weather-resistant outer tube, and a reinforcing fiber layer interposed between the inner and outer tubes. The rubber hose is connected at an end thereof to a nipple of a metallic pipe used in the engine room of a motor car, such that the hose's end is fitted on the nipple and externally tightened around the nipple with a fastening band. The inner tube of the rubber hose is formed of acrylonitrile-butadiene rubber (NBR), and the outer tube is formed of chlorosulphonated polyethylene (CSM), chlorinated polyethylene (CPE), or epichlorohydrin rubber (CHC), so that the inner and outer tubes have specified properties, specifically heat resistance, gasoline resistance and weather resistance.
Recently there is tendency that the engine room of a motor car is heated to a high temperature more than 100.degree. C., because engine fuel is required to be pressurized and heated to high level and degree for the purpose of exhaust gas control. Hence it is required that fuel transporting rubber hoses for use in a motor car engine room have a more excellent heat resistance. In addition, there has been encountered the problem that gasoline is subjected to oxidation due to the raised engine room temperature and consequently is changed to sour gasoline containing therein peroxides. The sour gasoline causes deterioration of the rubber hoses which serve for transporting it. Thus, it is also required that the fuel transporting rubber hoses have a high resistance to sour gasoline.
There is known another fuel transporting rubber hose the inner tube of which is formed of a fluoro rubber (FKM). This rubber hose has an excellent heat resistance and an excellent sour-gasoline resistance. However, the fluoro rubber is very expensive, and accordingly the cost of manufacture of the rubber hose is very high.
In this situation it has been proposed to provide a rubber hose the inner tube of which is constituted by two layers such that an inner layer of the inner tube is formed of FKM and an outer layer thereof is formed of a cheaper material. In the case where the outer layer is formed of CHC, the produced rubber hose has an excellent heat resistance. However, the cost of production of this rubber hose is not decreased to a sufficient low level. Meanwhile, in the case where NBR is used for forming the outer layer, the production cost is lowered to an appreciable level, but the heat resistance of the rubber hose is insufficiently low. Thus, there has not been provided a rubber hose which has an excellent heat resistance and which is produced at low cost. In other words, there is a great demand for a rubber hose which satisfies the two requirements of high heat resistance and low production cost.
There is known another problem with the use of FKM, namely, it is considerably difficult to vulcanize FKM to a different material with sufficient adhesive strength therebetween. In the case of the above-indicated rubber hose whose inner tube is constituted by two layers, the rubber hose suffers from insufficient adhesive strength between the inner and outer layers of the inner tube. In other words, the rubber hose is not free from the problem of peeling at the interface between the inner and outer layers of the inner tube.